1. Field of the Invention
The present invention relates to a wireless phone having an improved specific absorption rate (SAR).
2. Discussion of the Related Art
Examples of a wireless phone include cellular phones with the frequency band of 824–849 MHz and KPCS (Korea personal communication service) phones with the frequency band of 1750–1780 MHz and USPCS (US personal communication service) phones with the frequency band of 1850–1910 MHz based on the transmitting frequency.
The wireless phone that transmits and receives data based on the above frequency bands has problems in that its electromagnetic waves with high frequencies may be harmful to a human body as it is closely touched with an ear of a user.
Considering the harmful electromagnetic waves, many countries including Korea and USA have restricted SAR values to the brain of the human body within the range of 1.6 mW/g or below. In this respect, studies of a wireless phone having an improved SAR have actively advanced.
One example of a related art wireless phone will be described with reference to FIGS. 1 and 2.
Generally, a related art wireless phone includes a lower plate 120, an upper plate 130, and a hinge 103. The lower plate 120 and the upper plate 130 are opened and closed by the hinge 103. The lower plate 120 includes a lower frame case 108, a main board 106, and a battery 102. The main board 106 is built between the lower frame case 108 and a lower frame 104. The lower frame 104 is provided with an antenna that extends upwardly. The antenna is connected with the main board 106.
Meanwhile, the upper plate 130 includes a liquid crystal display (LCD) panel 109 provided between an upper frame case 113 and an upper frame 101. Since the LCD panel 109 and the main board 106 can be folded, a flexible printed circuit board (FPCB) 110 is interposed between them so as to connect them with each other. If the FPCB is connected with the LCD panel 109 by the hinge 103, some problems may occur. That is, a portion of the hinge 103 may become thick and fatigue ratio of the FPCB may increase. Therefore, it is general that the FPCB is connected with the LCD panel 109 by bypassing the hinge 103.
The aforementioned related art wireless phone should be grounded appropriately to remove electromagnetic wave noise caused by inductive electromotive force of the main board and the LCD panel. To this end, the board that constructs a circuit may be used as a ground plane, or a separate ground sheet may be provided. The LCD panel 109 is grounded using a connection terminal formed in the FPCB 10.
As aforementioned, if the wireless phone has a folder type, the FPCB 110 is provided far away from the hinge 103. The antenna 105 is provided on the outer edge of the hinge 103 so as to reduce the effect of the electromagnetic wave noise.
The current distribution of the related art wireless phone will be described with reference to FIG. 2.
The current distribution of the related art wireless phone shown in FIG. 2 was measured using an SAR measurement system which is a Swiss make Dosimetric Assessment System (Model No.: DASY3). In FIG. 2, it is noted that a hot spot on which strong electric field is concentrated exists within the lower plate 120 in which the antenna 105 is positioned. Slant lines in FIG. 2 belong to the hot spot.
As will be apparent from the expression, SAR=σ.E2/ρ(σ: conductive rate (s/m), E: electric field strength, ρ: tissue density (kg/m2), the SAR value is proportional to the electric field strength. Therefore, the greater the electric field strength is, the greater the SAR value is and the more harmful to the human body it is. For these reasons, the user is likely to be exposed to the strong electromagnetic wave in case of using the related art wireless phone.